1. Field of the Invention
The present invention relates to a method for polymerizing phosphorus-containing aromatic polyesters and more particularly to improvements in fire retardancy and chemical stability of a wholly aromatic polyester containing phosphorous compounds along with a method for polymerizing the same.
2. Description of the Prior Art
Generally, phosphorous compounds have been introduced into a main chain of an aromatic polyester by a skill known well to the art such as a solution polymerization method according to R. L. Holzberlein et al., in Polymer prepr., 30(1), 293(1989) which comprises heating a bisphenol and an aromatic dicarboxylic acid chloride in an organic solvent and a melt polymerization method which comprises heating a phenyl ester of an aromatic dicarboxylic acid and a bisphenol. However, when an aromatic polyester is produced by the solution polymerization method or the melt polymerization method, a high temperature or a reduced pressure is required. In addition, the aromatic polyesters produced by the aforementioned methods often show low molecular weights and are frequently discolored. Furthermore, the aromatic polyester according to both the conventional methods has not a sufficient fire retardancy and a satisfactory chemical resistance.